1. Field of the Invention
The present invention relates to a method and apparatus for matching streaked pattern images such as fingerprint images, and more particularly to a method and apparatus for matching streaked pattern images that can achieve higher accuracy when identifying fingerprints having few ending points and bifurcations.
2. Description of the Related Art
A variety of fingerprint matching methods have been proposed. For example, Japanese Patent Laid-Open Publication No. 59-778 (JP-A-59-778) discloses a matching method that employs the ending points and bifurcations in fingerprint ridges. These ending points and bifurcations are referred to as minutiae.
Japanese Patent Laid-Open Publication No. 2-224076 (JP-A-2-224076) (U.S. Pat. No. 4,947,442) discloses a matching method in which minutiae and non-minutiae are matched. In this matching method, when minutiae are not present in a small region of particular fixed area, the central coordinates of the small region are then used as non-minutiae. In addition, the assignee of the present application has also submitted an application for a method in which the areas of regions that are free of minutiae are used for matching.
U.S. Pat. No. 5,631,971 discloses a method in which matching is realized not only by positional and directional data of minutiae but also by some additional coded data detected by skeleton tracing in the vicinity of minutiae. These additional characteristics increase the information that can be used in matching.
In addition, Tetsuji Kobayashi discloses a method of matching fingerprints by skeletons in “A Fingerprint Verification Method Using Thinned Image Pattern Matching” in Transactions of the Institute of Electronics, Information and Communication Engineers (IEICE), D-II Vol. J79-D-II, No. 3, pp. 330-340 (March 1996). Skeletons are lines obtained by thinning the streaks such as the ridges of fingerprints.
U.S. Pat. No. 4,581,760 discloses a matching method in which image distortions are taken into consideration, the images being matched only for a plurality of partial regions.
Reducing the number of minutiae in a fingerprint that is the object of matching typically complicates matching. For example, the matching method that is disclosed in U.S. Pat. No. 5,631,971 assumes for the purpose of matching that a certain number of minutiae are present and that these minutiae have not been erroneously extracted. Matching is therefore problematic when few minutiae are present.
In addition, latent fingerprints that are to be matched are frequently distorted or have only a small area that can be used for matching, and matching is typically problematic when distortion occurs or when the area that can be used for matching is small. In the matching method described in the above-described paper by Kobayashi, for example, matching is possible when there is almost no distortion in the two fingerprints that are to be matched, but matching becomes difficult if there is distortion. The matching method that is described in U.S. Pat. No. 4,581,760 is difficult to apply when the area of a latent fingerprint is small.